Vehicle undercarriage

ABSTRACT

The invention relates to a vehicle undercarriage ( 1 ) or chassis for a vehicle, especially for a four-wheeled, driven vehicle for transporting at least one person. At least one main frame ( 2 ) is provided, said main frame ( 2 ) being configured as an arrangement of closed hollow profiles. The main frame ( 2 ) also has diametrically opposed torsion springs ( 4 ), whose axis of revolution runs crosswise in relation to the direction of travel. The torsion springs ( 4 ) are connected to side hollow profiles ( 3 ) of the main frame ( 2 ) with gusset plates ( 5 ). A flexurally resistant connecting pin ( 7 ) is provided on the torsion springs ( 4 ) with an oscillating lever ( 6 ), the connecting pin having a mounting ( 8 ) at its ends for the wheels.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Stage Application ofInternational Application No. PCT/AT99/00238 filed Oct. 5, 1999, andclaims priority of Austrian Patent Application No. A 1164/98, filed onOctober 6, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a vehicle undercarriage or chassis for avehicle especially for a four-wheeled, driven vehicle for transportingat least one person.

2. Discussion of Background Information

Vehicle carriages for multi-track motor vehicles, whereby the wheelsuspension is provided by torsion springs, are well known andwidespread. Thereby, a distinction must basically be made between twodifferent embodiments, namely the crank axle and the cam-lever shaft.

In the crank axle, the wheel axle is arranged on an elasticallyrotatable arm, whereby the arm changes its angle in relation to the axlesuspension with changing wheel load. The return torque usually increaseswith the change in angle, thus providing a rebound force on the wheelaxle that acts in the opposite direction of the forces of inertia. Theonly degree of freedom for movement in such an arrangement is theelastically limited rotation around the torsion spring element, so thatwith sufficiently stiff design of the arrangement a defined wheelguidance is obtained in the other directions of movement. The torsionspring element can be designed as a metal rod in the axis direction ofthe free rotational motion, or as an elastomer spring element that isdeformed primarily by shearing. Since each wheel is guided by a separatecrank guide, independent capability of movement of the wheels isachieved, i.e. independent wheel suspension. The crank axis representedhere is used preferably in load-bearing vehicles with relatively stiffsuspension. The torsion spring may have high torsion stiffness, so thatit has sufficient stiffness as a guiding element for the additionaldegrees of freedom of wheel movement. The disadvantage of thisembodiment is the fact that in passenger vehicles the suspension must besofter for reasons of comfort. However, with a softer suspension thetorsion spring can no longer manage the wheel guidance satisfactorily.Such inadmissible bump steers and camber changes under changing wheelloads lead to an unstable behavior of the vehicle.

In the embodiment with a cam-lever shaft, the spring energy is alsostored in a component that counters its twist with the relevant torque.It differs from the crank axle in that further directions of movementcan partly be restricted by separate elements. For example, embodimentsare known in which only longitudinal guidance of the wheel in thedirection of movement is achieved by the spring. Lateral guidance andmaintenance of the track and camber angle are provided by the split axleof the wheel drive. With this arrangement, stiff wheel guidance in alldirections except the compression is easier to achieve in terms ofconstruction. However, it is also possible to guide solely thecompression vertically to the tire contact area using the oscillatinglever, whilst defining all the other directions of movement with asuitable wheel suspension. The disadvantage of this design is the highconstruction cost, which also results in a high degree of failure.

SUMMARY OF THE INVENTION

The present invention provides a vehicle undercarriage of the typementioned at the beginning, which on the one hand avoids thedisadvantages described above and on the other hand makes use of theconstructional simplicity of the crank axle, whereby the restriction oflacking wheel guidance in the case of soft suspension is avoided.

The invention provides a vehicle undercarriage that includes at leastone main frame. The main frame is configured as an arrangement of closedhollow profiles and diametrically opposed torsion springs having axes ofrevolution crosswise to a direction of travel. The torsion springs areconnected to the lateral hollow profiles of the main frame with gussetplates, and a flexurally resistant connecting pin is provided on thetorsion springs with an oscillating lever. The connecting pin has amounting at its ends for the wheels.

The surprising advantage resulting from the above-noted features of theinvention lies in the fact that optimal wheel guidance that guaranteesstable driving behavior of the vehicle is achieved with an extremelysimple construction. By designing the main frame with hollow profilesjoined together in such a way as to be flexure- and torsion-resistant,the superstructure of the vehicle itself is also advantageouslytorsion-resistant. Moreover, the arrangement of the torsion springsoffers the advantage that in addition to a high degree of materialutilization for the elastic element of the suspension it is alsopossible to design wheel guidance functions using this suspension. Theflexurally stiff connecting pin is provided as wheel guidance element.In addition, this flexurally resistant connecting pin offers theadvantage that bump steer and camber change of the wheels are linkedmore or less rigidly by a connecting pin. Therefore, track width, toeangle and camber angle are invariant towards the plane through thecontact points of the wheels on the contact surface.

It is advantageous that an embodiment of the instant invention alsoincludes that all connections between the individual parts are madeexclusively with welding joints, since it allows rational manufacturing,possibly even with the use of welding robots.

In an advantageous embodiment the torsion spring includes of twoconcentrically arranged hollow profiles, whereby at least one elastomerelement is provided between the hollow profiles, preferably in the areaof mounting of the oscillating lever. In a further advantageousembodiment, the torsion spring includes an outer torsion spring tube, anelastomer spring element and a torsion spring axis. These torsionsprings provide a sufficient longitudinal stiffness in the direction oftheir axis of rotation and on the plane vertical to this axis.

In the embodiment in which the main frame includes of two lateral hollowprofiles and two torsion spring tubes configured as a roughlyring-shaped, flexure- and torsion-resistant arrangement, it is possibleto achieve optimal flexural and torsion stiffness for the main frame.

In a further embodiment, the connection between the lateral hollowprofiles and the torsion spring tubes or other connecting profiles isachieved by preferably flat gusset plates arranged on both sides of thelateral hollow profile. Thus, a torsion-resistant connection of thehollow profiles is achieved by the special arrangement of the gussetplates on both sides of the profile. The gusset plates are necessary inorder to connect at least two profiles with any connecting angle witheach other rigidly by means of welding. The profiles may have the samevertical parting sections. Unlike gusset plates in conventionalframework constructions, in the profile rods of which traction andpressure forces usually occur, flexural and torsion forces also have tobe transmitted in this construction.

The gusset plates should be arranged on both sides of the profiles sothat the welding seam is located in the neutral plane of the mainflexural stress of each connecting profile. As a result, expansionstress on the welding seam in such a case of stress can be avoided. Thisfact has an advantageous effect on the stability of the welding seam.

Due to the bilateral arrangement of the gusset plates on the connectingprofiles, however, stress with a general direction, such as e.g.flexion, torsion, traction or pressure, can be transferred without anunfavorable strain on the welding seams. The type and level of thecollective stress has a structural impact on the design of the gussetplate. The construction principle itself remains unaffected.

The advantage of this type of gusset connection includes the fact thatseparate profile sections, which are easy to manufacture, can be usedeven for complex framework geometries under any stresses vertical to theprofile axis.

The embodiment in which the connecting pin is configured as an openprofile with low torsion resistance in the area between the oscillatinglevers is also advantageous, since profiles of this type unite a highflexural resistance with low torsion resistance.

With the embodiment including a connecting pin having a flexure- andtorsion-resistant reinforcement in the area between the oscillatinglever (6) and the mounting (8), in particular the steering stub mountingand further embodiment including the connecting pin designed as a hollowprofile in the area between the oscillating lever and the mounting, inparticular the steering stub mounting, the torsion resistance of theconnecting pin can be varied in accordance with the length ofreinforcement, and it can be calculated in advance. Since the ratiobetween flexural stiffness and torsion resistance of a profile rod isvariable in many areas with the design of the profile cross-section, thewall thickness, dimensions and/or profile design, it is possible to linkthe individual compressions of an axle with each other. By increasingthe torsion resistance of the connecting pin accordingly, there isstronger coupling of the compression, so that the rolling angle of thevehicle, i.e. rotational movement around the longitudinal axis, can beprevented specifically. This is imperative especially in superstructuresthat create an elevated vehicle center of gravity.

Embodiments including the oscillating lever being connected rigidly tothe connecting pin; or including the oscillating lever being designed soas to have low torsion resistance along its longitudinal axis; orincluding the oscillating lever having a thin-walled, flat shape arealso advantageous. A variable compression invariably causes torsionalflexing of the connecting pin in relation to the vehicle superstructure.In this case, twisting is forced upon the oscillating levers, which areconnected rigidly to the connecting pin on the one hand, and canexclusively perform a rotational movement crosswise to the direction oftravel. Therefore, the oscillating levers should advantageously bedesigned so as to have low torsion resistance along the longitudinalaxis, in order to be able to achieve the necessary axle compression.This may be achieved with a thin-walled, flat design of the oscillatinglevers. Lateral forces such as those acting on the vehicle with everychange in direction would cause an inadmissible deformation of theoscillating levers crosswise to the direction of travel.

Thereby, an embodiment in which the rotation point of the oscillatinglever lies on the front connecting pin facing in the direction oftravel, on the line of efficacy between the overall center of gravity ofthe vehicle and the contact point of the wheels proves advantageous,since with the arrangement along this line the point of rotation of theoscillating lever is not additionally stressed by torque due to brakingforces during a braking maneuver using the front brakes, as a result ofwhich there is no spring feedback through the braking forces. Of coursethis arrangement is suitable both for front and rear axles.

An embodiment in which all the hollow profiles have vertical partingsections is also advantageous, since it guarantees rationalmanufacturing of components, whereby further processing is not required.

The embodiment in which a steering linkage is provided, including asteering rod lever connected rigidly to a steering rod, as well as arelay lever capable of swivelling on the steering rod lever around arotational axis parallel to the steering rod and which is connected toan eccentric shaft by a crank joint is particularly advantageous,whereby steering of the vehicle is independent of compression as aresult of the construction. Normally, the steering rod is connected tothe steering arms of the steering stubs via a ball joint. This allowssome degree of swivel movement of the steering rod around itlongitudinal axis. A relay lever arranged so as to be capable ofswivelling around an axis parallel to the steering rod can balance outspacing changes together with the steering lever. A steering lever ismounted rigidly on the steering rod with a hinge at the upper end, therotational axis of which is parallel to the steering rod. A relay leveris pivoted to the rotational axis of the steering lever, thus beingcapable of swivelling around an axis parallel to the steering rod. Therelay lever is connected to the eccentric shaft so as to be articulated.This construction transfers movements of the eccentric shaft parallel tothe steering rod directly to the joints of the steering stubs, but itcan balance out the changeable spacing of the eccentric shaft verticalto the steering rod.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is explained in more detail based on theembodiments illustrated in the figures.

The figures show the following:

FIG. 1 an oblique view,

FIG. 2 a side view,

FIG. 3 a top view of the vehicle undercarriage in accordance with theinvention, and

FIG. 4 part of the steering construction.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

By way of introduction, it is noted that in the described embodiment thesame parts are allocated the same reference numbers and the samecomponent names, whereby the disclosures contained throughout thedescription can be applied by analogy to the same parts with the samereference numbers or same component names. Furthermore, position detailsgiven in the description, e.g. top, bottom side, etc., relate to thefigures being described and illustrated at the time and with a change ofposition should be transferred accordingly to the new position.Furthermore, individual features of the illustrated embodiment maythemselves represent independent solutions in accordance with theinvention.

FIG. 1 shows an undercarriage 1 or chassis for a four-wheel motorizedvehicle for transportation of at least one person. In its basicconstruction, this vehicle undercarriage 1 comprises one main frame 2,which is made up of a more or less ring-shaped arrangement of closedhollow profiles. This main frame 2 is made preferably of two lateralhollow profiles 3 and two diametrically opposed torsion springs 4,whereby the rotational axes of the torsion springs 4 are arrangedcrosswise to the vehicle's direction of travel. With this embodiment ofthe main frame 2 with hollow profiles, a torsion-resistantsuperstructure of the vehicle is also possible. This is made possible bythe fact that each lateral hollow profile 3 of the main frame 2 isconnected to the torsion springs 4 so as to be flexion-andtorsion-resistant. This flexion and torsion resistance is achieved byproviding the connection preferably with plane gusset plates 5. Thegusset plates 5 are mounted bilaterally on the lateral hollow profiles3, whereby the welding joint is located on the neutral plane of the mainflexural stress of each connecting profile, in this case the lateralhollow profiles 3. Extension stresses on the welding joint can beavoided in such a case of stress, thus providing advantages with regardto the strength of the welding joint. In addition, a flexurally stiffconnecting pin 7 is provided at the torsion springs 4 via theoscillating lever 6. The connecting pin 7 has a mounting 8 for thewheels of the vehicles at its ends.

The lateral hollow profiles have fixtures 9 for the body of the vehiclearranged crosswise in relation to the direction of travel. Moreover,vertical supports 10 for this body can be arranged on the gusset plates5 for the rear torsion spring 4. Additional fixtures or bearing frames11 can, even if they project beyond the rear torsion spring 4, could bemounted on the main frame 2 and/or the supports 10 using the gussetplates 5.

The connecting pin 7 is designed as a torsion-elastic open profile 12 inthe area between the oscillating levers 6. In the area between theoscillating lever 6 and the mounting 7, a flexure- and torsion-resistantreinforcement 13 is provided, so that the type of reinforcement 13 cancreate a hollow profile. By choosing the length of the reinforcement 13accordingly, the torsion resistance of the connecting pin 7 can bevaried. Since the relation between flexural stiffness and torsionresistance of a profile rod, in this case of connecting pin 7, can bechanged by the design of the profile cross-section in many areas, it ispossible to link the individual compressions with each other on oneaxle. High torsion resistance leads to stronger coupling of thecompression, thus actively preventing rolling of the vehicle. Inaddition, this construction also permits controlled torsion of theconnecting pin 7.

The control panel 14 for steering the vehicle is mounted on the torsionspring 4, the front torsion spring facing in the direction of travel. Onthis control panel 14, which can be designed in two parts and each partof which is mounted close to the oscillating lever 6, a camshaft tube 15with an internal steering tube is mounted. A handlebar 17 is connectedto this steering tube 15 via a connecting element 16.

The general advantage of this type of construction is the fact that allthe connections between the individual components can be madeexclusively using welding joints. Moreover, it is technically optimaland rational in terms of manufacturing that all the hollow profiles,like for example the lateral hollow profile 3, the torsion spring 4 orthe connecting pin 7 have vertical parting sections.

In accordance with FIG. 2, the torsion springs 4 are attached to thelateral hollow profiles 3 via the gusset plates 5. Moreover, theoscillating levers 6 are provided on the torsion springs 4 for both thefront and the rear connecting pins 7. In addition, the bearing frame 11is provided on the support 10 or on the gusset plate for the rearrotational axis 4, for example for the cage of the vehicle. Equally, thecontrol panel 14 with the steering tube 15 and handlebar 17 is mountedon the front torsion spring 4.

The torsion spring 4 comprises two concentrically arranged hollowprofiles, whereby the outer hollow profile is a torsion spring tube 18and the inner hollow profile is a torsion spring axis 19. At least oneelastomer element 20 is arranged between the torsion spring tube 18 andthe torsion spring axis. With this arrangement of the torsion springs 4,sufficient longitudinal stiffness is achieved in the direction of itsrotational axis and the vertical plane in relation to.

The oscillating levers 6 are rigidly attached to the connecting pin 7.in addition, the oscillating levers are designed so as to have lowtorsion resistance along their longitudinal axis, and they have athin-walled, flat shape. As already mentioned, varying compressioninvariably causes torsional flexing of the connecting pin 7 in relationto the vehicle superstructure. In this case, twisting is forced upon theoscillating levers 6, which are connected rigidly to the connecting pin7, and can exclusively perform a rotational movement crosswise to thedirection of travel. Therefore, the oscillating levers 6 are designed soas to have low torsion resistance along the longitudinal axis, in orderto be able to achieve the necessary axle compression.

The rotation point 21 of the oscillating lever 6 lies on the frontconnecting pin 7 (facing in the direction of travel) on the—dotted—lineof efficacy between the overall center of gravity 22 of the vehicle andthe contact point 23 of the tires 24 on the wheels. Thus, the rotationpoint 21 of the oscillating lever 6 is not additionally subject totorque due to braking forces during a braking manuever with the brakes,and there is no spring feedback due to the braking forces.

In accordance with FIG. 3 the main frame 2 comprises the lateral hollowprofiles 3 and the torsion springs 4 has fittings 9 for the vehiclebody. The bearing frame 11 may project beyond the rear torsion spring 4facing in the direction of travel.

The connecting pin 7 is also mounted on the rear torsion spring 4 viathe oscillating lever 6. The connecting pin 7 can be offset, for examplefor mounting of the drive.

The front connecting pin 7 with the mounting 8 on both sides, inparticular in this case with a steering stub mounting 25 and thesteering construction, which is designed as a cassette construction, ismounted on the front tension spring 4. The steering constructionbasically comprises a steering rod 26, which is connected via a balljoint each to the steering levers 27 that can be arranged on both sides.The steering levers in turn are connected with steering stubs 28, whichform a unit with the connecting pin 7 via the steering stub mounting 25.Since the steering rod 26 is connected to the steering levers 27 of thesteering stub 28 via a ball joint 29, a certain scope of swivel movementof the steering rod 26 around its longitudinal axis is possible.

On the steering stubs 28, wheel hubs 30 are provided for the wheelbearings, whereby these wheel hubs 30 are fitted with braking discs 31.

FIG. 4 shows the steering construction in detail. A steering lever 32 ismounted rigidly on the steering rod 26, whereby a rotating joint 33, therotational axis 34 of which is parallel to the steering rod 26, isprovided at the upper end. On the rotating joint 33, a relay lever 35 ispivoted to the rotational axis 34 of the steering lever 32, thus beingcapable of swivelling around an axis parallel to the steering rod 26.The relay lever 35 is connected via a crank joint 36 to an eccentricshaft 37 that is attached to the steering tube 15.

This steering construction transmits movements of the eccentric shaft 37via the steering rod 26 and parallel to it directly to the joints formoving the wheels. In addition, this steering construction can balanceout the varying distance from the eccentric shaft 37 vertical to thesteering rod 26.

In conclusion, it is noted that for a better understanding of thesolution in accordance with the invention, the components areillustrated partly untrue to scale and/or are enlarged or illustratedschematically in the embodiments described above. Moreover, individualparts of the combination of features from the embodiment illustrated anddescribed can represent independent inventive solutions or solutionsaccording to the invention in themselves when combined with otherindividual features.

In particular, the individual embodiments illustrated in FIGS. 1 to 4can present individual solutions in accordance with the invention. Therelevant aims and solutions in accordance with the invention can befound in the detailed descriptions of these Figures.

List of references

1 Vehicle undercarriage

2 Main frame

3 Lateral hollow profile

4 Torsion spring

5 Gusset plate

6 Oscillating lever

7 Connecting pin

8 Mounting

9 Fixture

10 Support

11 Bearing frame

12 Profile

13 Reinforcement

14 Control panel

15 Steering tube

16 Connecting element

17 Handlebar

18 Torsion spring tube

19 Torsion spring axis

20 Elastomer element

21 Rotation point

22 Overall center of gravity

23 Contact point

24 Tire

25 Steering stub mounting

26 Steering rod

27 Steering lever

28 Steering stub

29 Ball joint

30 Wheel hub

31 Brake disk

32 Steering rod lever

33 Rotating joint

34 Rotational axis

35 Relay lever

36 Crank joint

37 Eccentric shaft

What is claimed is:
 1. A vehicle undercarriage or chassis for a vehiclecomprising: at least one main frame comprising an arrangement of closedhollow profiles in which two lateral hollow profiles and two torsionsprings are arranged as a roughly ring-shaped, flexure- andtorsion-resistant arrangement; gusset plates; said torsion springs beingdiametrically opposed with an axis of revolution extending crosswise toa direction of vehicle travel, and having outer tubes coupled to saidlateral hollow profiles via said gusset plates; oscillating levers; atleast one flexurally resistant connecting pin being coupled to saidtorsion springs via said oscillating levers, said connecting pin havingmountings, wherein each end of said connecting pin includes one of themountings and wherein each of the mountings is configured to receive awheel, whereby said connecting pin comprises a profile with low torsionresistance in an area between said oscillating levers and lowtorsion-resistance along a longitudinal axis.
 2. The vehicleundercarriage in accordance with claim 1, wherein said at least one mainframe is structured and arranged for a four wheeled vehicle fortransporting at least one person.
 3. The vehicle undercarriage inaccordance with claim 1, wherein connections between individual partsare made with welding joints.
 4. The vehicle undercarriage in accordancewith claim 1, wherein at least one of said torsion springs comprises twoconcentrically arranged hollow profiles, whereby at least one elastomerelement is positioned between said hollow profiles.
 5. The vehicleundercarriage in accordance with claim 4, wherein said at least oneelastomer element is positioned in a mounting area of at least one ofsaid oscillating levers.
 6. The vehicle undercarriage in accordance withclaim 1, wherein at least one of said torsion springs further comprisesan elastomer spring element and a torsion spring axis.
 7. The vehicleundercarriage in accordance with claim 1, further comprising additionalconnecting profiles and additional flat gusset plates, wherein saidadditional flat gusset plates are arranged on both sides of each of saidlateral hollow profiles to provide a connection between each of saidlateral hollow profiles and said additional connecting profiles.
 8. Thevehicle undercarriage in accordance with claim 1, wherein said gussetplates coupling said lateral hollow profiles to said torsion springs arearranged on both sides of each said lateral hollow profile.
 9. Thevehicle undercarriage in accordance with claim 1, wherein said at leastone connecting pin comprises an open profile in an area between saidoscillating levers.
 10. The vehicle undercarriage in accordance withclaim 1, wherein said at least one connecting pin comprises aflexure-and torsion-resistant reinforcement in an area between one ofsaid oscillating levers and one of the mountings.
 11. The vehicleundercarriage in accordance with claim 1, wherein at least one of saidmountings comprises a steering stub mounting.
 12. The vehicleundercarriage in accordance with claim 1, wherein said at least oneconnecting pin comprises a hollow profile in an area between one of saidoscillating levers and one of said mountings.
 13. The vehicleundercarriage in accordance with claim 1, wherein each of the mountingscomprises a steering stub mounting.
 14. The vehicle undercarriage inaccordance with claim 1, wherein said oscillating levers are rigidlycoupled to said at least one connecting pin.
 15. The vehicleundercarriage in accordance with claim 1, wherein each of saidoscillating levers comprises a thin-walled, flat shape.
 16. The vehicleundercarriage in accordance with claim 1, wherein said at least oneconnecting pin comprises a front connecting pin arranged to face in thetravel direction, a rotation axis of said oscillating levers lies onsaid front connecting pin on a line of efficacy between an overallcenter of gravity of the vehicle and a contact point of the wheelslocated at the front of the vehicle.
 17. The vehicle undercarriage inaccordance with claim 1, wherein each of said lateral hollow profiles iscoupled to a vertical parting section.
 18. The vehicle undercarriage inaccordance with claim 1, further comprising a steering linkagecomprising a steering rod lever rigidly coupled to a steering rod. 19.The vehicle undercarriage in accordance with claim 18, wherein saidsteering linkage further comprises a relay lever swivelably coupled tosaid steering rod lever around a rotational axis parallel to saidsteering rod, and said relay lever being coupled to an eccentric shaftby a crank joint.
 20. A vehicle undercarriage or chassis for a vehiclecomprising: two lateral closed hollow profiles and two torsion springsforming a main frame arrangement, the main frame arrangement being aflexure- and torsion-resistant arrangement; gusset plates connected tothe main frame arrangement; said two torsion springs being diametricallyopposed with an axis of revolution extending crosswise to a direction ofvehicle travel; each of said two torsion springs including an outer tubecoupled to said lateral hollow profiles via said gusset plates; twooscillating levers coupled to each of said two torsion springs; at leastone flexurally resistant connecting member being coupled to at least oneof said two torsion springs via said oscillating levers; said at leastone flexurally resistant connecting member having two ends wherein eachof said two ends has a mounting configured to receive a wheel; and saidat least one flexurally resistant connecting member comprising a profilewith low torsion resistance in an area between said oscillating leversand low torsion-resistance along a longitudinal axis.
 21. A vehicleundercarriage or chassis for a vehicle comprising: two lateral closedhollow profiles; a first torsion spring being coupled to a first end ofthe two lateral closed hollow profiles; a second torsion spring beingcoupled to a second end of the two lateral closed hollow profiles; thetwo lateral closed hollow profiles and the first and second torsionsprings forming a main frame that is flexure-and torsion-resistant; thefirst and second torsion springs being arranged to be diametricallyopposed with an axis of revolution extending crosswise to a direction ofvehicle travel; each of the first and second torsion springs having anouter tube coupled to said lateral closed hollow profiles via gussetplates; two oscillating levers coupled to the first torsion spring; twooscillating levers coupled to the second torsion spring; a firstflexurally resistant connecting member being coupled to the firsttorsion spring via said two oscillating levers; a second flexurallyresistant connecting member being coupled to the second torsion springvia said two oscillating levers; each of the first and second flexurallyresistant connecting members having two ends wherein each of said twoends has a mounting configured to receive a wheel; and at least one of:the first flexurally resistant connecting member comprising a profilewith low torsion resistance in an area between said two oscillatinglevers and low torsion-resistance along a longitudinal axis; and thesecond flexurally resistant connecting member comprising a profile withlow torsion resistance in an area between said two oscillating leversand low torsion-resistance along a longitudinal axis.